Traffic signals, also referred to as traffic lights or stop lights, are signaling devices generally positioned at an intersection between two or more roads, paths, crosswalks, tracks, etc. to control flows of traffic competing to enter to the intersection.
In order to control which flow of traffic can enter the intersection, each traffic signal produces a well-known color code to notify each user, e.g., vehicle operator, pedestrian, etc., at the intersection whether the user may proceed through the intersection.
For example, traffic signals at roadway intersections generally consist of three lights: red, amber (commonly referred to as yellow), and green. The red light, when illuminated, indicates to a vehicle operator that he must stop at the intersection until the green light or yellow light is illuminated. The yellow light, when illuminated, indicates to a vehicle operator entering an intersection that he has “right-of-way” access to the intersection, and that he may cross the intersection, but must proceed with caution in doing so. The yellow light may indicate an intermediate state in a transition from green to red. The green light, when illuminated, also indicates to a vehicle operator that he has right-of-way access, and can safely enter the intersection.
It is important that traffic signals operate to promote vehicle and pedestrian safety by controlling conflicting flows of traffic at an intersection in an organized manner with minimal delay at the intersection, which can otherwise lead to traffic congestion, or result in personal injury or vehicle damage caused by collisions at the intersection by aggressive drivers “running the red light,” or caused by vehicles abruptly stopping at the intersection when improperly notified of an impending red light.
In addition, traffic congestion at intersections results in wasteful fuel consumption. In fact, some studies have shown in an average of 60 hours of delay per year per driver results from such congestion. In the United States alone, over 2.9 billion gallons of gasoline are consumed each year due to traffic congestion. The environmental impact is also an issue, with automobile exhaust containing air pollutants, such as carbon dioxide (CO2) being emitted while drivers sit idle. For example, each gallon of gasoline burned can add approximately 19.5 lbs of CO2 to the atmosphere.
Traffic planning engineers are often retained to study such traffic congestion issues and to provide solutions to these issues in order to improve traffic flow, and thereby reduce traffic congestion.
One approach used by traffic planning engineers to manage traffic flows through a succession of intersections is to coordinate the timing of traffic signals at the intersections, which permits a higher volume of traffic to safely move through the intersections with fewer stops and minimal acceleration and braking. However, vehicle operator behavior is difficult to predict and operator responses to well-timed signals can be erratic, misguided, and possibly conflict with the goals of a traffic planning engineer.
FIG. 1 is a graph illustrating various driver behaviors when proceeding through four successive traffic signals A-D.
As shown in FIG. 1, vehicle 1 passes through a first traffic signal A in a green signal state, i.e., the green light is illuminated, but is driving considerably fast such that vehicle 1 approaches a subsequent second traffic signal B in a red signal state, i.e., the red light is illuminated. Vehicle 2 likewise passes through the first traffic signal A in a green signal state, but is driving considerably slower, so that vehicle 2 also approaches a subsequent second traffic signal B in a red signal state. Thus, while traffic signals A-D are timed for vehicles that drive within a predetermined range of speeds, vehicles that drive too fast or too slow, such as vehicles 1 and 2, are likely to encounter a traffic signal in a red signal state, not a preferable green signal state. Vehicle 3, for example, travels at an optimal speed that permits vehicle 3 to enter each intersection when each corresponding traffic signal A-D is in the green signal state. Since there is no way for the operator of vehicle 3 to know when a given traffic signal will enter a red signal state, vehicle 3 must rely on the proper timing of the traffic signals and a presumption that the speed limit represents the optimal speed, assuming unabated travel. However, unabated travel at the speed limit from one traffic signal to the next is rarely achievable. Slowdowns and stoppages between traffic signals are commonplace.